Excimers are diatomic molecules or complexes of molecules that have stable excited states with an unbound or weakly bound ground state. In principle, they can be formed by all rare gases and rare-gas halogen mixtures and in most cases, the reaction kinetics leading to the excimer is selective. Because these complexes are unstable, they disintegrate within a few nanoseconds converting their excitation energy to spontaneous optical emission. Re-absorption of this light cannot occur because these complexes have no stable ground state. In turn, it is possible to construct excimer lamps emitting light with a high intensity within narrow spectral regions in the deep uv. Many materials absorb radiation at less than approximately 250 nm, making uv or vuv sources important. In turn, these sources can selectively drive radical-mediated processes such as: uv curing, metal depositions, protective and functional coating, pollution control, photo-deposition of amorphous semiconductors, and photo-deposition of dielectric layers.
Many different electrical discharge techniques have been used to drive excimer emission. Such techniques include dielectric barrier discharge, uv preionization, microwave discharge, pulsed longitudinal discharges, continuous longitudinal discharge, nuclear excitation, and hollow cathode discharge. Alexandrovich et al. (B. M. Alexandrovich, R. B. Piejak, V. A. Godyak, "Frequency Dependence of RF-Driven Subminiature Fluorescent Lamp," Journal of the Illuminating Engineering Society, Vol. 25, No. 1, p. 93-99, (1996)) describe capacitively coupled rf discharges for electrodeless subminiature fluorescent lamps with mercury/argon gas mixtures. However, they fail to report the use of capacitively coupled rf discharge to produce excimer emission.
Previous rf designs were configured to avoid electrodes internal to the plasma, the dominant capacitively or inductively coupled designs employ external tunable inductors and/or capacitors to create an impedance match between a tuned cavity and the power supply. Such designs require precise tuning.
Lamps that have strong emissions in the 180 nm-200 nm region are desirable because of the responsiveness of organic materials in this wavelength range. Previous argon/fluorine lamp mixtures, although producing emissions at 193 nm, were limited in utility because the fluorine attacked the quartz from which the bulbs are usually made. Lamps based on the 190 nm krypton/iodine excimer face the problem of iodine condensation. In turn, it is desirable to have a lamp containing a gas capable of forming an electronically excited molecular state that can be contained with a center conductor without producing adverse reactions or side-effects.
It is an object of the present invention to provide an rf capacitively-coupled electrodeless light source.
A further object of the present invention is to provide an rf capacitively-coupled electrodeless light source that incorporates a tuner as both part of the cabling to the power supply in addition to serving as an integral part of the lamp cavity.
Another object of the present invention is to provide an rf capacitively-coupled electrodeless light source that eliminates the need for precise tuning.